Acidification is not involved in the early inhibition of Staphylococcus aureus growth by Lactococcus lactis in milk

Investigating lactic acid bacteria genus Lactococcus lactis properties: Antioxidant activity, antibiotic resistance, and antibacterial activity against multidrug-resistant bacteria Staphylococcus aureus

Background

Lactic acid bacteria (LAB) are utilized as a starter culture in the manufacturing of fermented dairy items, as a preservative for various food products, and as a probiotic. In our country, some research has been carried out, even if LAB plays a principal role in food preservation and improves the texture and taste of fermented foods, that is why we tried to evaluate their probiotic effect. The objective of this research was to determine the antibacterial activity of Lactococcus lactis (L. lactis) against Staphylococcus aureus (S. aureus) ATCC 29213, investigate their antioxidant activity, and characterize their sensitivity against 18 antibiotics.

Methods

A total of 23 LAB (L. lactis subsp. cremoris, L. lactis subsp. Lactis diacetylactis, L. lactis subsp. lactis) were isolated from cow's raw milk. The antibacterial activity was performed using two techniques, competition for nutrients and a technique utilizing components nature, using the disk diffusion method. The sensitivity of the studied LAB to different antibiotics was tested on Man rogosa sharp (MRS) agar using commercial antibiotic disks. All strains of LAB were examined for their antioxidant activity. The antioxidant activity of L. lactis was tested by 2,2-diphenyl-1 picrylhydrazyl (DPPH).

Results

The results showed that the MRS medium was more adapted than Muller Hinton Agar (MHA) to investigate the antibacterial activity of L. lactis against S. aureus ATCC 29213. Also, L. lactis exhibited a notable degree of antibacterial activity against S. aureus ATCC 29213. L. Lactis subsp. Lactis displayed higher antibacterial activities, followed by L. lactis ssp. lactis biovar. diacetylactis, and lastly, L. lactis ssp. cremoris against S. aureus ATCC 29213. Lc 26 among all strains of L. lactis showed a high potential antibacterial activity reaching 40 ± 3 mm against S. aureus ATCC 29213. All strains of L. lactis showed a slightly moderate antioxidant activity (10.56 ± 1.28%-26.29 ± 0.05 %). The results of the antibiotic resistance test indicate that all strains of L. lactis were resistant to cefotaxime, sulfamethoxazole-trimethoprim, and streptomycin and were sensitive to Ampicillin, Amoxicillin, Penicillin G, Teicoplanin, Vancomycin, Gentamicin 500, Tetracycline, and Chloramphenicol. These test results indicate that this strain falls within the criteria of not posing any harmful effects on human health. The important antibacterial properties recorded for all L. Lactis strains were derived from the production of antibacterial active metabolites, such as protein, diacetyl, hydrogen peroxide, and lactic acid, together with the fight for nutrients.

Conclusion

This study suggests that the strains of L. lactis could be added as an antibacterial agent against S. aureus ATCC 29213 and can provide an important nutritional property for their antioxidant potential.

Growth of methicillin-resistant Staphylococcus aureus during raw milk soft cheese-production and the inhibitory effect of starter cultures

The consumption of raw milk or raw milk products might be a potential risk factor for the transmission of methicillin-resistant Staphylococcus aureus (MRSA). Therefore, we studied MRSA growth during raw milk soft cheese-production. Furthermore, we investigated the inhibitory effect of four starter cultures (Lactococcus lactis, Lacticaseibacillus rhamnosus, Lactiplantibacillus plantarum, Lactobacillus helveticus) on the growth of MRSA in a spot-agar-assay and in raw milk co-culture following a cheesemaking temperature profile. During the initial phases of raw milk cheese-production, MRSA counts increased by 2 log units. In the ripening phase, MRSA counts only dropped slightly and remained high up to the end of the storage. Comparable MRSA counts were found in the rind and core and strain-specific differences in survival were observed. In the spot-agar-assay, all four starter cultures showed strong or intermediate inhibition of MRSA growth. In contrast, in raw milk, only Lactococcus lactis strongly inhibited MRSA, whereas all other starter cultures only had minor inhibitory effects on MRSA growth. Our results indicate that MRSA follow a similar growth pattern as described for other S. aureus during raw milk soft cheese-production and illustrate the potential use of appropriate starter cultures to inhibit MRSA growth during the production of raw milk cheese.

Genomic analysis and in vivo efficacy of Pediococcus acidilactici as a potential probiotic to prevent hyperglycemia, hypercholesterolemia and gastrointestinal infections

Lactic acid bacteria are the well acknowledged probiotics that can cure a variety of diseases. In this study, we observed the in vivo potentials of Pediococcus to treat hyperglycemia, hypercholesterolemia and gastrointestinal infections. A total of 77 Lactobacillus were isolated from the milk of 10 cows and 10 goats, four of those strains inhibited both carbohydrates-hydrolyzing enzymes, α-glucosidase, and α-amylase. They all showed antagonistic effects on pathogenic E. coli and S. Typhimurium which were confirmed by performing pathogen challenge test and visualizing on Electron microscopy. 16S rRNA gene sequence identified that all four strains belong to Pediococcus genus which were further distinguished as Pediococcus acidilactici by pheS gene sequence. Whole genome sequence analysis revealed their non-pathogenic properties for human and the presence of probiotic genes responsible for stress resistance, immunomodulation, adhesion, metal and drug resistance. In vivo trial with diabetes-induced mice ascertained that all Pediococcus acidilactici had significant potentials to reduce elevated glucose and low-density lipoprotein level in blood. Interestingly, two out of four strains were significantly more effective (p < 0.0001 each) than metformin in reducing the blood glucose level. This in vivo study demonstrated that Pediococcus acidilactici might be a promising probiotic to prevent hyperglycemia, hypercholesterolemia and gastrointestinal infections.

Enhancement of low-fat Feta cheese characteristics using probiotic bacteria

The objective of this study was to manufacture low-fat Feta cheese (LFC) using different types of starter cultures, such as yogurt (Y) cultures (Streptococcus thermophilus and Lactobacillus bulgaricus), bifidobacterium (B) cultures (Bifidobacterium bifidum and Bifidobacterium longum), and mixed of them (Y + B) at different rates (0.4, 0.5, and 0.6%). The Y + B cultures improved the flavor and body and texture of LFC, especially at a ratio of 0.4 + 0.6% and 0.5 + 0.5%, which is similar to the typical full-fat Feta cheese. Also, the LFC maintained a higher number of probiotics and lactic acid bacteria after 30 d of storage at a range of 5 to 7 log cfu/g.

In vitro screening of probiotic properties of Lactobacillus plantarum isolated from fermented milk product

Objectives

The screening of traditional fermented products is essential for the assessment of safety, security, and further development of functional foods for the well-being of human health. The aim of the present study was to isolate and identify bacteria from fermented raw milk samples that exhibit health benefits upon consumption.

Methods

In order to confirm the isolates as probiotics, several in vitro assays were conducted to assess the probiotic properties of isolated bacteria. The initial screening includes tolerance to acid, bile, pancreatin, and NaCl. The cell surface properties demonstrate their interaction with mucosal epithelium, which includes hydrophobicity and auto-aggregation assay. Safety assessment was done by performing haemolytic test and antibiotic susceptibility test. The antagonistic activity of probiotic strain was further evaluated against some pathogenic bacteria.

Results

Lactobacillus plantarum (L. plantarum) isolated from fermented raw milk was preliminarily identified by biochemical tests and further confirmed using 16S rRNA identification. The isolate designated as L. plantarum strain GCC_19M1 demonstrated significant tolerance to low pH, 0.3% bile, 0.5% pancreatin, and 5% NaCl. In the presence of simulated gastric juice (at pH 3), the isolate exhibited a survival rate of 93.48–96.97%. Furthermore, the development of ecological niches in the human gut and their successful accumulation have been revealed by auto-aggregation and hydrophobicity properties. Absence of haemolytic activity ensures the non-virulent nature of the strain. Lactobacillus plantarum strain GCC_19M1 showed susceptibility towards gentamicin, tetracycline, kanamycin, meropenem, and ceftriaxone and exhibited an antagonistic effect on pathogenic bacteria.

Conclusion

The obtained results conveyed that L. plantarum strain GCC_19M1 has strong probiotic potential, and its presence in the fermented raw milk products may serve as a potent functional probiotic food.

The effect of protective cultures on Staphylococcus aureus growth and enterotoxin production

Staphylococcus aureus is the causative agent of staphylococcal food poisoning and is a common contaminant in milk. Despite efforts to control S. aureus, recalls and outbreaks continue to occur, highlighting the need for additional interventions. This study determined the potential for protective cultures (PC) that are commercially available to producers to control S. aureus growth in raw milk and attenuate virulence by impeding staphylococcal enterotoxin (SE) production in raw milk and laboratory medium. Cultures of Hafnia alvei and Lactococcus lactis effectively inhibited S. aureus growth in raw milk to counts ~5 log CFU/mL lower than control when cocultured following a cheesemaking time and temperature profile; two cultures of Lactobacillus plantarum inhibited growth to ~1.5 log CFU/mL less than control. Cocultures of S. aureus with Lc. lactis, H. alvei and Lb. plantarum in raw milk reduced SE levels by 24.9%, 62.4%, and 76%, respectively. Lc. lactis also decreased SE production in raw milk in the absence of PC-mediated growth inhibition. Significant reductions in SE production in the absence of pathogen growth inhibition were also achieved in laboratory medium. Together, these results demonstrate the potential for PCs to inhibit S. aureus growth and impede SE production in the absence of growth inhibition.

Viability of Staphylococcus aureus and expression of its toxins (SEC and TSST-1) in cheeses using Lactobacillus rhamnosus D1 or Weissella paramesenteroides GIR16L4 or both as starter cultures

Staphylococcus aureus is one of the main causative agents of food poisoning. This bacterium is an important component of cheese microbiota and plays an important role in foodborne diseases. Another important component of the microbiota is the lactic acid bacterium, which actively participates in processes that define the physicochemical, sensorial, and microbiological features of cheese. Of the various microbiological interactions in cheese, the interaction between lactic acid bacteria and Staph. aureus is most relevant. To this end, we evaluated the viability of Staph. aureus strains and the expression of their enterotoxins in cheeses produced experimentally, using Weissella paramesenteroides GIR16L4 or Lactobacillus rhamnosus D1 or both as starter cultures. Over 7 d, we observed that the presence of lactic acid bacteria did not impair Staph. aureus growth. However, via qPCR we observed a change in the gene expression of staphylococcal enterotoxins, suggesting that molecular communication exists between Staph. aureus strains and lactic acid bacteria in cheese.

Dialogue between Staphylococcus aureus SA15 and Lactococcus garvieae strains experiencing oxidative stress

Background

Staphylococcus aureus is an important foodborne pathogen. Lactococcus garvieae is a lactic acid bacterium found in dairy products; some of its strains are able to inhibit S. aureus growth by producing H₂O₂. Three strains of L. garvieae from different origins were tested for their ability to inhibit S. aureus SA15 growth. Two conditions were tested, one in which H₂O₂ was produced (high aeration) and another one in which it was not detected (low aeration). Several S. aureus genes related to stress, H₂O₂-response and virulence were examined in order to compare their level of expression depending on the inoculated L. garvieae strain. Simultaneous L. garvieae H₂O₂ metabolism gene expression was followed.

Results

The results showed that under high aeration condition, L. garvieae strains producing H₂O₂ (N201 and CL-1183) inhibited S. aureus SA15 growth and impaired its ability to deal with hydrogen peroxide by repressing H₂O₂-degrading genes. L. garvieae strains induced overexpression of S. aureus stress-response genes while cell division genes and virulence genes were repressed. A catalase treatment partially or completely restored the SA15 growth. In addition, the H₂O₂ non-producing L. garvieae strain (Lg2) did not cause any growth inhibition. The SA15 stress-response genes were down-regulated and cell division genes expression was not affected. Under low aeration condition, while none of the strains tested exhibited H₂O₂-production, the 3 L. garvieae strains inhibited S. aureus SA15 growth, but to a lesser extent than under high aeration condition.

Conclusion

Taken together, these results suggest a L. garvieae strain-specific anti-staphylococcal mechanism and an H₂O₂ involvement in at least two of the tested L. garvieae strains.

Electronic supplementary material

The online version of this article (10.1186/s12866-018-1340-3) contains supplementary material, which is available to authorized users.

Staphylococcus aureus undergoes major transcriptional reorganization during growth with Enterococcus faecalis in milk

Previous studies have demonstrated the antagonistic potential of lactic acid bacteria (LAB) present in raw milk microbiota over Staphylococcus aureus, albeit the molecular mechanisms underlying this inhibitory effect are not fully understood. In this study, we compared the behavior of S. aureus ATCC 29213 alone and in the presence of a cheese-isolated LAB strain, Enterococcus faecalis 41FL1 in skimmed milk at 30 °C for 24 h using phenotypical and molecular approaches. Phenotypic analysis showed the absence of classical staphylococcal enterotoxins in co-culture with a 1.2-log decrease in S. aureus final population compared to single culture. Transcriptional activity of several exotoxins and global regulators, including agr, was negatively impacted in co-culture, contrasting with the accumulation of transcripts coding for surface proteins. After 24 h, the number of transcripts coding for several metabolite responsive elements, as well as enzymes involved in glycolysis and acetoin metabolism was increased in co-culture. The present study discusses the complexity of the transcriptomic mechanisms possibly leading to S. aureus attenuated virulence in the presence of E. faecalis and provides insights into this interspecies interaction in a simulated food context.

Growth, nisA Gene Expression, and In Situ Activity of Novel Lactococcus lactis subsp. cremoris Costarter Culture in Commercial Hard Cheese Production

This study evaluated in situ expression of the nisA gene by an indigenous, nisin A-producing (NisA+) Lactococcus lactis subsp. cremoris raw milk genotype, represented by strain M78, in traditional Greek Graviera cheeses under real factory-scale manufacturing and ripening conditions. Cheeses were produced with added a mixed thermophilic and mesophilic commercial starter culture (CSC) or with the CSC plus strain M78 (CSC+M78). Cheeses were sampled after curd cooking (day 0), fermentation of the unsalted molds for 24 h (day 1), brining (day 7), and ripening of the brined molds (14 to 15 kg each) for 30 days in a fully controlled industrial room (16.5°C; 91% relative humidity; day 37). Total RNA was directly extracted from the cheese samples, and the expression of nisA gene was evaluated by real-time reverse transcription PCR (qRT-PCR). Agar overlay and well diffusion bioassays were correspondingly used for in situ detection of the M78 NisA+ colonies in the cheese agar plates and antilisterial activity in whole-cheese slurry samples, respectively. Agar overlay assays showed good growth (>8 log CFU/g of cheese) of the NisA+ strain M78 in coculture with the CSC and vice versa. The nisA expression was detected in CSC+M78 cheese samples only, with its expression levels being the highest (16-fold increase compared with those of the control gene) on day 1, followed by significant reduction on day 7 and almost negligible expression on day 37. Based on the results, certain intrinsic and mainly implicit hurdle factors appeared to reduce growth prevalence rates and decrease nisA gene expression, as well as the nisin A-mediated antilisterial activities of the NisA+ strain M78 postfermentation. To our knowledge, this is the first report on quantitative expression of the nisA gene in a Greek cooked hard cheese during commercial manufacturing and ripening conditions by using a novel, rarely isolated, indigenous NisA+ L. lactis subsp. cremoris genotype as costarter culture.

Probiotic potential of Lactobacilli with antagonistic activity against pathogenic strains: An in vitro validation for the production of inhibitory substances

BACKGROUND

Probiotics, live cells with different beneficiary characteristics, have been extensively studied and explored commercially in many different products in the world. Their benefits to human and animal health have proven in hundreds of scientific studies. Based on rich bibliographic material, Curd is the potential source of probiotic Lactobacilli.

METHOD

The aim of the present study was to observe Lactobacilli with probiotic potential activities from different curd samples for isolation, identification and characterization of Lactobacillus species.

RESULTS

Among the samples, thirty lactic acid bacterial strains were isolated, sixteen (16/30) best Lactobacillus isolates were selected by preliminary screening as potential probiotic for acid and bile tolerance, further confirmed using 16s rRNA identification. All the selected Lactobacillus isolates were then characterized in vitro for their probiotic characteristics and antimicrobial activities against pathogens and aggregation studies. The results indicated that selected potential probiotic isolates (T2, T4 and T16) were screened and confirmed as Lactobacillus. The isolates produced positive tolerance to excited pH, NaCl and bile salts, also revealed noticeable antimicrobial activities against pathogens. All the Lactobacillus isolates were susceptible to clinical antibiotics used. Besides, T2 isolate was constituted to retain stronger auto and co-aggregation and cell surface hydrophobicity capacity.

CONCLUSION

Based on the drawn results, T2, T4 and T16 Lactobacillus isolates were recognised as ideal, potential in vitro antimicrobial probiotic isolates against pathogens and studies are needed further in-vivo assessment and human health benefits in their real-life situations.

Secretion of biologically active pancreatitis-associated protein I (PAP) by genetically modified dairy Lactococcus lactis NZ9000 in the prevention of intestinal mucositis

Background

Mucositis is one of the most relevant gastrointestinal inflammatory conditions in humans, generated by the use of chemotherapy drugs, such as 5-fluoracil (5-FU). 5-FU-induced mucositis affects 80% of patients undergoing oncological treatment causing mucosal gut dysfunctions and great discomfort. As current therapy drugs presents limitations in alleviating mucositis symptoms, alternative strategies are being pursued. Recent studies have shown that the antimicrobial pancreatitis-associated protein (PAP) has a protective role in intestinal inflammatory processes. Indeed, it was demonstrated that a recombinant strain of Lactococcus lactis expressing human PAP (LL-PAP) could prevent and improve murine DNBS-induced colitis, an inflammatory bowel disease (IBD) that causes severe inflammation of the colon. Hence, in this study we sought to evaluate the protective effects of LL-PAP on 5-FU-induced experimental mucositis in BALB/c mice as a novel approach to treat the disease.

Results

Our results show that non-recombinant L. lactis NZ9000 have antagonistic activity, in vitro, against the enteroinvasive gastrointestinal pathogen L. monocytogenes and confirmed PAP inhibitory effect against Opportunistic E. faecalis. Moreover, L. lactis was able to prevent histological damage, reduce neutrophil and eosinophil infiltration and secretory Immunoglobulin-A in mice injected with 5-FU. Recombinant lactococci carrying antimicrobial PAP did not improve those markers of inflammation, although its expression was associated with villous architecture preservation and increased secretory granules density inside Paneth cells in response to 5-FU inflammation.

Conclusions

We have demonstrated for the first time that L. lactis NZ9000 by itself, is able to prevent 5-FU-induced intestinal inflammation in BALB/c mice. Moreover, PAP delivered by recombinant L. lactis strain showed additional protective effects in mice epithelium, revealing to be a promising strategy to treat intestinal mucositis.

Transcriptomic and metabolic responses of Staphylococcus aureus in mixed culture with Lactobacillus plantarum, Streptococcus thermophilus and Enterococcus durans in milk

Staphylococcus aureus is a major food-borne pathogen due to the production of enterotoxin and is particularly prevalent in contaminated milk and dairy products. The lactic acid bacteria (LAB) are widely used as biocontrol agents in fermented foods which can inhibit pathogenic flora. In our work, we investigated the influence of three strains of LAB (Lactobacillus plantarum, Streptococcus thermophilus and Enterococcus durans) on the relative expression of three enterotoxin genes (sea, sec, sell) and eight virulence and/or regulatory genes (sarA, saeS, codY, srrA, rot, hld/RNAIII, agrA/RNAII, sigB) in two S. aureus strains (MW2 and Sa1612) in TSB and reduced-fat milk (1.5 %) at 30 °C over a 24-h period. The tested LAB and S. aureus strains proved to be mutually non-competitive or only slightly competitive during co-cultivation. In addition, under the above-mentioned conditions, differential gene expression between the S. aureus MW2 and Sa1612 strains was well documented. S. aureus growth was changed in mixed culture with LAB; however, its effect on the repression of sea and sec expression correlated with production of these virulence factors. In comparison, the presence of LAB strains generally inhibited the expression of sec, sell, sarA, seaS, agrA/RNAII and hld/RNAIII genes. The effect of LAB strains presence on the expression of sea, codY, srrA, rot and sigB genes was medium, time, LAB and S. aureus strain specific. SEA and SEC production was significantly reduced in milk compared to TSB in pure culture. After the 24-h cultivation, S. aureus MW2 and Sa1612 SEC production was 187 and 331 times lower in milk compared to TSB, respectively (0.07 and 0.39 ng/mL in milk, versus 13.1 and 129.2 ng/mL in TSB, respectively). At the same time S. aureus MW2 and Sa1612 SEA production was 77 and 68 times lower in milk compared to TSB, respectively (0.99 and 0.17 ng/mL in milk, versus 76.4 and 11.5 ng/mL in TSB, respectively). This study has revealed new insights into the interaction between S. aureus and LAB (L. plantarum, S. thermophilus, E. durans) on the level of the expression and/or production of S. aureus enterotoxins, regulatory and virulence genes in different media, including milk. This study provides data which may improve the quality of food production.

Lactococcus lactis V7 inhibits the cell invasion of bovine mammary epithelial cells by Escherichia coli and Staphylococcus aureus

Bovine mastitis, an inflammatory disease of the mammary gland often associated to bacterial infection, is the first cause of antibiotic use in dairy cattle. Because of the risk of antibioresistance emergence, alternative non-antibiotic strategies are needed to prevent or to cure bovine mastitis and reduce the antibiotic use in veterinary medicine. In this work, we investigated Lactococcus lactis V7, a strain isolated from the mammary gland, as a probiotic option against bovine mastitis. Using bovine mammary epithelial cell (bMEC) culture, and two representative strains for Escherichia coli and for Staphylococcus aureus, two major mastitis pathogens, we investigated L. lactis V7 ability to inhibit cell invasion (i.e. adhesion and internalization) of these pathogens into bMEC. L. lactis V7 ability to modulate the production of CXCL8, a key chemokine IL-8 responsible for neutrophil influx, in bMEC upon challenge with E. coli was investigated by an ELISA dosage of CXCL8 in bMEC culture supernatants. We showed that L. lactis V7 inhibited the internalisation of both E. coli and S. aureus strains into bMEC, whereas it inhibited the adhesion of only one out of the two S. aureus strains and of none of the E. coli strains tested. Investigation of the bMEC immune response showed that L. lactis V7 alone induced a slight increase in CXCL8 production in bMEC and that it increased the inflammatory response in bMEC challenged with the E. coli strains. Altogether these features of L. lactis V7 make it a potential promising candidate for a probiotic prevention strategy against bovine mastitis.

Behavior of Staphylococcus aureus in culture broth, in raw and thermized milk, and during processing and storage of traditional Greek Graviera cheese in the presence or absence of Lactococcus lactis subsp. cremoris M104, a wild, novel nisin A-producing raw milk isolate

This study was conducted to evaluate the behavior of Staphylococcus aureus during processing, ripening, and storage of traditional Greek Graviera cheese in accordance with European Union Regulation 1441/2007 for coagulase-positive staphylococci in thermized milk cheeses. Lactococcus lactis subsp. cremoris M104, a wild, novel nisin A-producing (NisA+) strain, also was evaluated as an antistaphylococcal adjunct. A three-strain cocktail of enterotoxigenic (Ent+) S. aureus increased by approximately 2 log CFU/ml when co-inoculated (at approximately 3 log CFU/ml) in thermized Graviera cheese milk (TGCM; 63°C for 30 s) with commercial starter culture (CSC) and/or strain M104 at approximately 6 log CFU/ml and then incubated at 37°C for 3 h. However, after 6 h at 37°C, significant retarding effects on S. aureus growth were noted in the order TGCM + M104 > TGCM + CSC = TGCM + CSC + M104 > TGCM. Additional incubation of TGCM cultures at 18°C for 66 h resulted in a 1.2-log reduction (P < 0.05) of S. aureus populations in TGCM + M104. The Ent + S. aureus cocktail did not grow but survived during ripening and storage when inoculated (at approximately 3 log CFU/g) postcooking into Graviera mini cheeses prepared from TGCM + CSC or TGCM + CSC + M104, ripened at 18°C and 90% relative humidity for 20 days, and stored at 4°C in vacuum packages for 2 months. A rapid 10-fold decrease (P < 0.05) in S. aureus populations occurred within the first 24 h of cheese fermentation. Reductions of S. aureus were greater by approximately 0.4 log CFU/g in CSC + M104 than in CSC only cheeses, concomitantly with the presence of NisA + M104 colonies and nisin-encoding genes in the CSC plus M104 cheeses and their corresponding microbial consortia only. A high level of selective survival of a naturally nisin-resistant EntC z S. aureus strain from the cocktail was noted in CSC + M104 cheeses and in coculture with the NisA + M104 strain in M-17 broth. In conclusion, although S. aureus growth inhibition is assured during Graviera cheese ripening, early growth of the pathogen during milk curdling and curd cooking operations may occur. Nisin-resistant S. aureus strains that may contaminate Graviera cheese milks postthermally may be difficult to control even by the application of the NisA + L. lactis subsp. cremoris strain M104 as a bioprotective adjunct culture.

Production of Staphylococcus aureus enterotoxin a in raw milk at high temperatures

Improper processing and storage of raw milk contaminated with Staphylococcus aureus at elevated temperatures can result in the production of staphylococcal enterotoxins, especially type A (SEA), which is most frequently associated with food poisoning outbreaks such as the large one in Osaka, Japan, in 2000. In this study, the characteristics of S. aureus growth and SEA production at various high temperatures in raw milk samples were studied using two raw milk samples naturally containing low and high levels of natural microflora. The optimal temperatures found for SEA production in the two milk types were as high as 40 and 44°C (range, 36 to 48°C), and SEA production was dependent on the initial dose of S. aureus. These high temperatures were close to that of the outbreak in Japan. Thus, it was concluded that temperature was critical for SEA production in raw milk. It was also observed that natural microflora in the milk samples considerably suppressed SEA production but not staphylococcal growth. On the other hand, the amount of toxin in most milk samples decreased after peaking during storage.

Fate of enterotoxigenicStaphylococcus aureusand staphylococcal enterotoxins in Feta and Galotyri cheeses

In this study the fate of enterotoxigenicStaphylococcus aureusand staphylococcal enterotoxins in Feta and Galotyri cheeses were studied. Initially, the enterotoxigenic abilities of fourStaph. aureusLHA, LHB, LHC and LHD strains isolated from raw ovine milk were examined in both BHI broth and ovine milk. In BHI broth, theStaph. aureusLHA, LHB, LHC and LHD strains were found toxigenic at 37 °C producing the staphylococcal enterotoxins (SEs) serotypes SEA, SEB, SEC and SED, respectively, whereas in ovine milk at 37 °C,Staph. aureusLHD was found to produce only SED, while no SE production was observed for the other examined strains. Thus, the fate of onlyStaph. aureusLHD and SED were examined in Feta and Galotyri cheeses. The cheeses were made from raw ovine toxic milk with preformed SED or raw ovine milk contaminated with high (ca 6 log cfu/ml) and low inocula (ca 3 log cfu/ml) ofStaph. aureusLHD. Results showed that the pathogen was eliminated at slower rate in Galotyri cheese than in Feta cheese, for the high (5 d vs. 16 d) or the low (1 d vs. 12 d) inoculum trials. In both cheeses produced from the toxic milk, SED was detected during manufacturing and storage. SED was also detected in the curd (2 h), whenStaph. aureusLHD populations had reached ca 7 log cfu/g, and up to the end of storage for the high inoculum trials of both cheeses. No SED was observed for the low inoculum trials of either cheese.

Monitoring of a gluten content in selected meat products from three biggest meat producers in Slovakia

The work is focused on a monitoring of a gluten content in selected meat products from three biggest and most popular meat producers in Slovakia. Gluten is a type of protein complex which is typical naturally presented component of wheat, barley and rye. Flour from this sources with natural gluten content is also added into the some type of meat products and other foodstuffs for a technological reasons hand in hand with economic reasons.  Some of the gluten quantities could be hazardous for sensitive people as celiatics and allergic to gluten. Within the context of this reasons there is a need to control the amounts of this hidden type of gluten inclusive of spice mixes using in a meat production. Monitoring by itself was realized with a use of the sandwich ELISA RIDASCREEN® Fast Gliadin test. ELISA means enzyme linked immunosorbent assay. It is based on a specific reaction among the enzyme and antigen leading to a creation of a complex.  This test provides us exact quantitification of a gluten content in this type of food products using a colorimetric reaction of a complex by observing of all fundamentals of this technique. There were analysed 16 meat products and 5 types of spice mixes in total.

Staphylococcus aureus virulence and metabolism are dramatically affected by Lactococcus lactis in cheese matrix

In complex environments such as cheeses, the lack of relevant information on the physiology and virulence expression of pathogenic bacteria and the impact of endogenous microbiota has hindered progress in risk assessment and control. Here, we investigated the behaviour of Staphylococcus aureus, a major foodborne pathogen, in a cheese matrix, either alone or in the presence of Lactococcus lactis, as a dominant species of cheese ecosystems. The dynamics of S. aureus was explored in situ by coupling a microbiological and, for the first time, a transcriptomic approach. Lactococcus lactis affected the carbohydrate and nitrogen metabolisms and the stress response of S. aureus by acidifying, proteolysing and decreasing the redox potential of the cheese matrix. Enterotoxin expression was positively or negatively modulated by both L. lactis and the cheese matrix itself, depending on the enterotoxin type. Among the main enterotoxins involved in staphylococcal food poisoning, sea expression was slightly favoured in the presence of L. lactis, whereas a strong repression of sec4 was observed in cheese matrix, even in the absence of L. lactis, and correlated with a reduced saeRS expression. Remarkably, the agr system was downregulated by the presence of L. lactis, in part because of the decrease in pH. This study highlights the intimate link between environment, metabolism and virulence, as illustrated by the influence of the cheese matrix context, including the presence of L. lactis, on two major virulence regulators, the agr system and saeRS.

Staphylococcus aureus and Listeria monocytogenes in Norwegian raw milk cheese production

The aim of this study was to survey the presence of Staphylococcus aureus and Listeria monocytogenes during the cheese making process in small-scale raw milk cheese production in Norway. The prevalence of S. aureus in bovine and caprine raw milk samples was 47.3% and 98.8%, respectively. An increase in contamination during the first 2-3 h resulted in a 73.6% prevalence of contamination in the bovine curd, and 23 out of 38 S. aureus-negative bovine milk samples gave rise to S. aureus-positive curds. The highest contamination levels of S. aureus were reached in both caprine and bovine cheese after 5-6 h (after the first pressing). There was no contamination of L. monocytogenes in caprine cheeses and only one (1.4%) contaminated bovine cheese. This work has increased our knowledge about S. aureus and L. monocytogenes contamination during the process of raw milk cheese production and gives an account of the hygiene status during the manufacture of Norwegian raw milk cheeses.

Staphylococcus aureus virulence expression is impaired by Lactococcus lactis in mixed cultures

Staphylococcus aureus is responsible for numerous food poisonings due to the production of enterotoxins by strains contaminating foodstuffs, especially dairy products. Several parameters, including interaction with antagonistic flora such as Lactococcus lactis, a lactic acid bacterium widely used in the dairy industry, can modulate S. aureus proliferation and virulence expression. We developed a dedicated S. aureus microarray to investigate the effect of L. lactis on staphylococcal gene expression in mixed cultures. This microarray was used to establish the transcriptomic profile of S. aureus in mixed cultures with L. lactis in a chemically defined medium held at a constant pH (6.6). Under these conditions, L. lactis hardly affected S. aureus growth. The expression of most genes involved in the cellular machinery, carbohydrate and nitrogen metabolism, and stress responses was only slightly modulated: a short time lag in mixed compared to pure cultures was observed. Interestingly, the induction of several virulence factors and regulators, including the agr locus, sarA, and some enterotoxins, was strongly affected. This work clearly underlines the complexity of L. lactis antagonistic potential for S. aureus and yields promising leads for investigations into nonantibiotic biocontrol of this major pathogen.